Glucagon, gastric inhibitory polypeptide and the gastrocolic response

Serosal bipolar electrodes and strain gauge force transducers were placed on the right and left colon in subhuman primates to record spike discharges and circular muscular contractions. The effect of glucagon on colonic motor and electrical activity were studied before and after meals. Serum concentration of gastric inhibitory polypeptide was measured simultaneously 15 minutes before and 45 minutes after eating. Serum levels of gastric inhibitory polypeptide increased in response to eating; pre- and postcibal concentrations were not altered by glucagon. The gastrocolic response of the colon to eating was demonstrated. Glucagon inhibited the intrinsic activity of the entire colon before meals and partly inhibited the right colon after meals. Postcibal left colon activity was not inhibited by glucagon. This indicates that a distinct mechanism accounts for the left colonic postcibal increase in contractile and electrical spike activity. A neural or humoral mechanism is implicated but is not specifically identified.